During the second year of the project the system of detecting mitotic nondisjunction and crossing-over will be expanded to the detection of meiotic nondisjunction and translocations. The mitotic system is rapid and sensitive and does nor rely on cytological observations. Instead, genetic markers are examined by replica plating conidia from abnormally growing aneuploid colonies induced by a test compound. These "abnormal" colonies have recognizable phenotypes, characteristic of the special linkage group which is responsible for the aneuploidy. In the detection of translocations diploid strains will be exposed to mutagens during germination and then haplodized; the chromosomes involved in the translocation would be expected to show linkage of the appropriate markers. In each approach to detecting chromosomal aberrations quantitation of the event will be sought. The products of the events, however, are clonally distributed; hence, the factors which determine the relationship between the number of mutagenic events and the actual observable products will have to be delineated. If successful in the aforementioned studies, chemical compounds will be selected for screening.